Aluminum nitride (AlN) holds great promise as a semiconductor basis material for numerous applications, e.g., opto-electronic devices such as short-wavelength LEDs and lasers, dielectric layers in optical storage media, electronic substrates, and chip carriers where high thermal conductivity is essential, among many others. In principle, the properties of AlN will allow light emission in the 200 nm wavelength region to be achieved. But many practical difficulties should be addressed for such devices to become commercially practicable.
For example, bulk AlN crystals often exhibit a substantial amount of cracking, which results in crystal separation before, during or after the crystal is formed into a wafer. If the crystal cracks or fully separates, it is very difficult or sometimes impossible to use it as a reliable substrate for device fabrication. Most of the commercially available machines for epitaxy, photolithography and other device processing require perfectly shaped, round wafers with uniform thickness. Any crack, even ones that do not result in wafer separation, will impair commercial usefulness. Therefore, the cracking problem in AlN crystal growth has crucial importance for the further development of nitride-based electronics.
In addition, many opto-electronic applications will require transparent wafers. While AlN is intrinsically transparent at optical wavelengths between 210 and 4500 nm, macroscopic defects such as cracks and inclusions significantly scatter light and reduce the apparent transparency in this important optical region. Elimination of cracks and inclusions is of critical importance to the development of ultraviolet light emitting diodes (LEDs), for example.